Halogens can act as electrophiles to attack a double bond in alkene. Double bond represents a region of electron density and therefore functions as a nucleophile. 

In organic chemistry, an electrophilic addition reaction is an addition reaction where, in a chemical compound, a π bond is broken and two new σ bonds are formed. The substrate of an electrophilic addition reaction must have a double bond or triple bond.

Electrophilic addition reaction:
An electrophilic addition reaction is a type of organic reaction in which an electrophile reacts with a nucleophile, resulting in the addition of new atoms to a molecule. In the case of alkenes, which are unsaturated hydrocarbons with carbon-carbon double bonds, the addition of halogens is an example of an electrophilic addition reaction.

Halogenation of alkenes:
The addition of halogens, such as chlorine or bromine, to alkenes is known as halogenation. This reaction occurs due to the electrophilic nature of the halogens and the nucleophilic nature of the alkene.

Mechanism of halogenation:
The halogenation of alkenes proceeds through a three-step mechanism known as electrophilic addition.

1. Activation: The alkene acts as a nucleophile and attacks the electrophilic halogen molecule, causing the formation of a cyclic halonium ion intermediate. This step is highly exothermic and involves the breaking of the π bond in the alkene.

2. Nucleophilic attack: The cyclic halonium ion intermediate is unstable and highly reactive. A nucleophile, such as a halide ion (X-), attacks the cyclic halonium ion, resulting in the formation of a dihaloalkane. The nucleophilic attack occurs at the carbon atom that was originally part of the double bond.

3. Regeneration of the catalyst: The final step involves the regeneration of the catalyst, which is the halogen molecule. The halide ion that participated in the nucleophilic attack donates its electrons to the positively charged halonium ion, resulting in the release of the dihaloalkane product.

Key points:
- The addition of halogens to alkenes is an example of an electrophilic addition reaction.
- The reaction proceeds through a three-step mechanism involving activation, nucleophilic attack, and regeneration of the catalyst.
- Halogenation of alkenes results in the formation of dihaloalkanes.
- This reaction is used in various industrial processes and plays a significant role in organic synthesis.

In conclusion, the addition of halogens to alkenes is an example of an electrophilic addition reaction. This reaction involves the activation of the alkene, nucleophilic attack by a halide ion, and regeneration of the halogen catalyst. Halogenation of alkenes is an important reaction in organic chemistry and finds applications in various fields.